This research project is investigating the cause, prevention, and treatment of infections of prosthetic heart valves. The bacterium, Staphylococcus epidermidis, has been used as the focus of this study because it is the most common organism causing prosthetic valve endocarditis. Studies specifically involve investigating the mechanisms of antimicrobial resistance among endocarditis isolates, the use of an experimental animal model to study prophylaxis and therapy, the investigation of antibody to the organism in the serum of infected animals, and studies of the epidemiology of the organism of the skin of patients undergoing valve replacement.